1. Field of the Invention
This invention relates to power generation systems and, more particularly, to feedwater and cooldown water discharge apparatus for use in nuclear power system steam drums, and the like.
2. Description of the Prior Art
In nuclear power plants, as well as in other steam generation systems, it is usually necessary to separate moisture from the steam that is generated within the system in order to produce the "dry" steam needed to drive the turbines and other plant machinery. This separation usually is carried out in the steam drum which encloses an array of devices that are frequently referred to as "steam separators".
In certain types of nuclear reactor systems, for example, the steam drum is mounted directly above and in fluid communication with a heat exchanger. In this arrangement, the water in the heat exchanger absorbs heat from the primary reactor coolant. The water then rises into steam that flows upwardly through the heat exchanger and into the steam drum for moisture separation. For a number of reasons, the feedwater is introduced into the system by means of a tubular ring that is positioned in the transition between the heat exchanger and the steam drum. This ring has a number of holes and is spaced inwardly of the walls of the transition in order to discharge the feedwater through the holes and into an annular chamber that encloses the steam generating section of the heat exchanger.
This particular feature of prior steam drums has been a source of difficulty. In this respect, the cold feedwater striking the relatively thick, hot steel pressure vessel, or shell, that encloses the heat exchanger frequently produces undesirable and potentially destructive stresses. The tubular ring also presents a number of problems. Thus, for a marine or shipboard installation the ring arrangement is quite unsatisfactory during rolling or listing conditions. The ring also must be mounted securely within the transition. In spite of this obvious need for a secure mounting, the ring nevertheless must be able to respond to thermal expansion and contraction without bulging or becoming permanently deformed. Because this ring is mounted in the transistion between the heat exchanger and the steam drum, the ring tends to obstruct the flow of steam and moisture into some of the separators in the steam drum.
There is a further need to provide an emergency spray of cooling water for the heat exchanger in the event a leak occurs and feedwater is lost. This emergency spray should remove residual heat from the heat exchanger and prevent thermal damage to the heat exchanger structure. Ordinarily, provision is made for introducing this "cooldown" spray through a conduit that penetrates the transition wall. The conduit terminates at the longitudinal axis of the heat exchanger in a 90.degree. bend with an attached spray head. The spray head directs the cooldown fluid into the central portion of the heat exchanger in the event of a loss of coolant accident. Thus, there usually are two means for supplying the heat exchanger with fluids, the cooldown conduit and the feedwater ring, the ring, moreover, presenting a number of difficult problems. Accordingly, there is a need to improve fluid delivery systems for heat exchangers.